1. Field of the Invention
The present invention generally relates to an apparatus for measuring fine particles contained in superpurified water and other liquids used for washing and the like in, for example, the manufacturing process of integrated circuits.
2. Description of the Prior Art
Superpurified water and the like containing fine particles at a remarkably small ratio has been used as water for washing and other uses in the manufacturing process of integrated circuits. An apparatus for measuring fine particles contained in such superpurified water and other liquids has been disclosed in, for example, Japanese Utility Model Laid-Open No. 189251/1986.
This conventional apparatus for measuring fine particles contained in liquids comprises a nozzle disposed at one end of a cylindrical cell in a direction of the axial shaft line thereof. The nozzle supplies an inside of the cell with water to be measured and a pipe disposed at the other end of the cylindrical cell discharges the water to be measured. Light-transmitting windows are disposed at opposite positions in a radial direction of the cell; a detection window is disposed at a position meeting at nearly right angles with a line between the windows; and an optical detector is disposed outside of the detection window through an optical system. In addition, a light-emitting means is disposed outside of the light-transmitting window.
In the measurement of fine particles by this conventional apparatus, water to be measured is spouted into the cell from the nozzle and discharged through a discharge pipe. A light, such as a helium-neon laser beam, emitted from the light-emitting means passes through the cell through a pair of light-transmitting windows disposed in an opposite relation, but the light passing through this cell also passes through the water to be measured which was spouted from the nozzle.
Accordingly, if fine particles are contained in the water to be measured, the light is scattered by the fine particles. This light, which was scattered by the fine particles and then transmitted through the detection window, is detected by an optical detector through the optical system. A number and a grain size of the fine particles are measured on the basis of the detected light.
With the conventional apparatus for measuring fine particles, a Gaussian distribution of the laser beam passing through water to be measured and which spouted from the nozzle is strong in a central portion in the radial direction thereof and weak toward both side portions. Thus, the strength of the light scattered by the fine particles, which passed by both side portions of the laser beam, is not proportional to the grain size of the fine particles. Moreover, the strength of the light scattered by the fine particles is inversely proportional to a speed of the fine particles, while a flow rate of water to be measured which spouted from the nozzle is reduced in a circumferential portion of the nozzle in comparison with a central portion of the nozzle.
With the conventional apparatus, the light scattered by the fine particles contained in water to be measured is detected at a position on a side portion of water to be measured which spouted from the nozzle.
Accordingly, since the light scattered by the fine particles contained in both side portions of water to be measured opposite to the optical system is also detected in the partial measurement in which the measurement for both side portions of water to be measured opposite to the optical system is excluded, a problem occurs in that the resolution of grain size is reduced, whereby it is difficult to measure the grain size of the fine particles having a grain size of about 0.4 microns or less.
Accordingly, it has been difficult to presume the kind of fine particles, place where the fine particles are contained and the like, and utilize the measured results for preventing the fine particles from being contained.